A tank-integrated shroud is for example disclosed in JP-A-2001-317357. A tank, which is used as a resonator, is integrated with a shroud by utilizing a free space around the shroud. Specifically, as shown in FIG. 5, a tank 320a has an opening portion 322 on one side. The opening portion 322 is welded to a wall 311a of a shroud 310. The wall 311a is provided by an air guiding portion 311. Also, a looped projection 312, corresponding to the periphery of the opening portion 322, is formed on the flat wall 311 so that the opening portion 322 is easily welded. However, because the shroud 310 has a generally flat box shape, the air guiding portion 311 is flat.
Regarding the air guiding portion of the shroud, generally, it is preferable to have a bell-mouth shape curving from the peripheral portion of the shroud toward a fan 301 so that air flows smoothly, as shown in FIG. 6. However, when the air guiding portion 311 has the flat shape as of the above-mentioned shroud, the flow of air is likely to be disturbed, as shown in FIGS. 7A and 7B. As a result, an air blow performance is deteriorated. Further, the above construction causes noise problem. FIG. 7A shows an example where a tank volume is small. FIG. 7B shows an example where a tank volume is large.